program f90_KAIKI
    implicit none
    integer::i,ndata,nt
    real(8),allocatable::datax(:),datay(:)
    real(8)::aa,bb,rr

    ndata=8
    nt=ndata
    allocate(datax(1:ndata),datay(1:ndata))

    do i=1,ndata
        datax(i)=dble(i)
        datay(i)=dble(2*i+2)
    end do

    call KAIKI(ndata,datax,datay,aa,bb,rr,nt)

    write(6,'("y=aa*x+bb")')
    write(6,'("aa=",e15.7)') aa
    write(6,'("bb=",e15.7)') bb
    write(6,'("rr=",e15.7)') rr

stop

contains

    subroutine KAIKI(ndata,datax,datay,aa,bb,rr,nt)
        integer,intent(in)::ndata,nt
        real(8),intent(in)::datax(1:nt),datay(1:nt)
        real(8),intent(out)::aa,bb,rr

        integer::i
        real(8)::x1,y1,x2,xy,xm,ym,c1,c2,c3

        !回帰式：y=aa*x+bb
        x1=0.0D0
        y1=0.0D0
        x2=0.0D0
        xy=0.0D0
        do i=1,ndata
            x1=x1+datax(i)
            y1=y1+datay(i)
            x2=x2+datax(i)*datax(i)
            xy=xy+datax(i)*datay(i)
        end do
        xm=x1/dble(ndata)
        ym=y1/dble(ndata)
        aa=(dble(ndata)*xy-x1*y1)/(dble(ndata)*x2-x1*x1)
        bb=(x2*y1-x1*xy)/(dble(ndata)*x2-x1*x1)
        c1=0.0D0
        c2=0.0D0
        c3=0.0D0
        do i=1,ndata
            c1=c1+(datax(i)-xm)*(datay(i)-ym)
            c2=c2+(datax(i)-xm)*(datax(i)-xm)
            c3=c3+(datay(i)-ym)*(datay(i)-ym)
        end do
        rr=c1/sqrt(c2*c3)

    end subroutine KAIKI

end program f90_KAIKI